Category: BESSY II at HZB

Nanoislands on silicon with switchable topological textures

Nanoislands on silicon with switchable topological textures

Nanostructures with specific electromagnetic patterns promise applications in nanoelectronics and future information technologies. However, it is very challenging to control those patterns. Now, a team at HZB examined a specific class of nanoislands on silicon with interesting chiral, swirling polar textures, which can be stabilised and even reversibly switched by an external electric field.

Ferroelectrics at the nanoscale exhibit a wealth of polar and sometimes swirling (chiral) electromagnetic textures that not only represent fascinating physics, but also promise applications in future nanoelectronics. For example, ultra-high-density data storage or extremely energy-efficient field-effect transistors. However, a sticking point has been the stability of these topological textures and how they can be controlled and steered by an external electrical or optical stimulus.

New perspectives:

A team led by Prof. Catherine Dubourdieu (HZB and FU Berlin) has now published a paper in Nature Communications that opens up new perspectives. Together with partners from the CEMES-CNRS in Toulouse, the University of Picardie in Amiens and the Jozef Stefan Institute in Ljubljana, they have thoroughly investigated a particularly interesting class of nanoislands on silicon and explored their suitability for electrical manipulation.

Nanoislands on silicon

“We have produced BaTiO3 nanostructures that form tiny islands on a silicon substrate,” explains Dubourdieu. The nano-islands are trapezoidal in shape, with dimensions of 30–60 nm (on top), and have stable polarisation domains. “By fine tuning the first step of the silicon wafer passivation, we could induce the nucleation of these nanoislands,” says Dong-Jik Kim, a scientist in Dubourdieu’s team.

Read more on HZB website

Image: Artistic representation of the center down-convergent polarization field. It results from the compression of the polarization flux by the sidewalls of the nanoislands. The texture in each nanoisland resembles a swirling vortex of liquid flowing into a narrowing funnel.

Credit: Laura Canil /HZB

Lithium-sulphur pouch cells investigated at BESSY II

Lithium-sulphur pouch cells investigated at BESSY II

A team from HZB and the Fraunhofer Institute for Material and Beam Technology (IWS) in Dresden has gained new insights into lithium-sulphur pouch cells at the BAMline of BESSY II. Supplemented by analyses in the HZB imaging laboratory and further measurements, a new picture emerges of processes that limit the performance and lifespan of this industrially relevant battery type. The study has been published in the prestigious journal Advanced Energy Materials.

Lithium-sulphur batteries have a number of advantages over conventional lithium batteries: they use the abundant raw material sulphur, do not require the critical elements cobalt or nickel, and can achieve extremely high specific energy densities. Prototype cells are already achieving up to 500 Wh/kg, almost twice as much as current lithium-ion batteries.

Degradation processes examined

However, lithium-sulphur batteries have so far been much more susceptible to degradation processes: during charging and discharging, dissolved polysulphides and sulphur phases form on the lithium electrode, gradually reducing the performance and lifetime of the battery. ‘Our research aims to elucidate these processes in order to improve this type of battery,’ says HZB physicist Dr. Sebastian Risse, who leads a team at HZB working on operando analysis of batteries.

The pouch cell lab at HZB

He is focusing on pouch cells, a battery format widely used in industry. HZB’s Institute for Electrochemical Energy Storage (CE-IEES), headed by Prof. Yan Lu, has therefore set up a laboratory specialising in the production of lithium-sulphur batteries in the required pocket format. Here, scientists can produce and investigate a wide variety of lithium-sulphur pouch cells. As part of the BMBF-funded ‘SkaLiS’ project, coordinated by Sebastian Risse, a team from the Fraunhofer Institute for Material and Beam Technology (IWS) in Dresden has now published a comprehensive study of lithium-sulphur pouch cells in the prestigious journal Advanced Energy Materials.

Multimodal setup

The battery cells were studied in a setup developed at HZB using various methods such as impedance spectroscopy, temperature distribution, force measurement and X-ray imaging (synchrotron and laboratory source) during charging and discharging. For the first time, we were able to observe and document both the formation of lithium dendrites and the dissolution and formation of sulphur crystallites during multi-layer battery operation,’ says Dr Rafael Müller, HZB chemist and first author of the study.

Read more on HZB website

Image: Photomontage: the diagonal line divides the image into a photo of the lithium-sulfur pouch cell (left) and the corresponding X-ray image (right) during the multimodal measurement with force sensor (golden) and temperature sensors. The perforated honeycomb structure of the current collector can be clearly seen on the X-ray image. This new design approach reduces the weight of the cell without compromising performance.

Credit: R. Müller/ HZB

Ultrafast dissociation of molecules studied at BESSY II

Ultrafast dissociation of molecules studied at BESSY II

For the first time, an international team has tracked at BESSY II how heavy molecules – in this case bromochloromethane – disintegrate into smaller fragments when they absorb X-ray light. Using a newly developed analytical method, they were able to visualise the ultrafast dynamics of this process. In this process, the X-ray photons trigger a “molecular catapult effect”: light atomic groups are ejected first, similar to projectiles fired from a catapult, while the heavier atoms – bromine and chlorine – separate more slowly.

When X-rays hit molecules, they can knock electrons out of certain orbitals and into extremely high-energy states, breaking chemical bonds. This often happens ultra rapidly, in just a few femtoseconds (10-15 s). While this phenomenon has been studied in light molecules such as ammonia, oxygen, hydrochloric acid or simple carbon compounds, it has hardly been studied in molecules with heavier atoms.

A team from France and Germany has now studied the rapid decay of molecules containing halogens. They focused on a molecule in which bromine and chlorine atoms are linked by a light bridge – an alkylene group (CH2). The measurements were made at the XUV beamline of BESSY II.

Read more on HZB website

Image: The X-ray photons trigger a ‘molecular catapult effect’: light atomic groups are ejected first, similar to projectiles shot from a catapult, while the heavier atoms – bromine and chlorine – separate much more slowly. The image was printed on the cover of “The Journal of Physical Chemistry Letters”.

Credit: The Journal of Physical Chemistry Letters

Battery research with the HZB X-ray microscope

Battery research with the HZB X-ray microscope

New cathode materials are being developed to further increase the capacity of lithium batteries. Multilayer lithium-rich transition metal oxides (LRTMOs) offer particularly high energy density. However, their capacity decreases with each charging cycle due to structural and chemical changes. Using X-ray methods at BESSY II, teams from several Chinese research institutions have now investigated these changes for the first time with highest precision: at the unique X-ray microscope, they were able to observe morphological and structural developments on the nanometre scale and also clarify chemical changes.

Lithium-ion batteries are set to become even more powerful with new materials for the cathodes. For example, layered lithium-rich transition metal (LRTMO) cathodes could further increase the charge capacity and be used in high-performance lithium batteries. However, so far it has been observed that these cathode materials ‘age’ rapidly: the cathode material degrades as a result to the back-and-forth migration of lithium ions during charging and discharging. Until now it was unclear what specific changes these would involve.

Teams from Chinese research institutions have therefore applied for beam time at the world’s only transmission X-ray microscope (TXM) at an undulator beamline at the BESSY II storage ring to investigate their samples using 3D tomography and nanospectroscopy. The HZB-TXM measurements were performed by Dr. Peter Guttmann, HZB, back in 2019, before the coronavirus pandemic. The X-ray microscopic analysis was then supplemented by further spectroscopic and microscopic examinations. After careful evaluation of the extensive data, the results are now available: they provide detailed information on changes in the morphology and structure of the material, but also on chemical processes during discharge.

‘Soft X-ray transmission microscopy allows us to visualise chemical states in LRTMO particles in three dimensions with high spatial resolution and to gain insights into chemical reactions during the electrochemical cycle,’ explains Dr Stephan Werner, who is responsible for the scientific supervision and further development of the instrument.

Read more on HZB website

Image: The left side of the figure shows nanotomography images of an LRTMO particle taken at the TXM of BESSY II before the first charging cycle (top) and after 10 charging cycles (bottom). In the simulation (right side), the isolated pores are highlighted in light blue. After 10 charging cycles, the number of pores and cracks has significantly increased.

Credit: HZB

New procedure for better thermoplastics

New procedure for better thermoplastics

Bio-based thermoplastics are produced from renewable organic materials and can be recycled after use. Their resilience can be improved by blending bio-based thermoplastics with other thermoplastics. However, the interface between the materials in these blends sometimes requires enhancement to achieve optimal properties. A team from the Eindhoven University of Technology in the Netherlands has now investigated at BESSY II how a new process enables thermoplastic blends with a high interfacial strength to be made from two base materials: Images taken at the new nano station of the IRIS beamline showed that nanocrystalline layers form during the process, which increase material performance.

Bio-based thermoplastics are considered environmentally friendly, as they are sourced from non-petroleum-based raw materials and can be recycled just like standard thermoplastics. A thermoplastic base material is Polylactic acid (PLA), which can be produced from sugar cane or corn. Researchers around the world are working to optimise the properties of PLA-based plastics, for example by mixing them with other thermoplastic base materials. However, this is a real challenge.

A new process for better blends

Now, a team from the TU Eindhoven led by Prof. Ruth Cardinaels is showing how PLA can be successfully mixed with another thermoplastic. They developed a process in which certain PLA-based copolymers (e.g. SAD) are formed during production, which facilitate the mixing of the two raw materials by forming particularly stable (stereo)-crystalline layers at the interfaces between the different polymer phases (ICIC strategy).

Insights at the IRIS-Beamline

At BESSY II, they have now discovered which processes ensure that the mechanical properties of the mixed thermoplastic are significantly better. To do so, they examined pure 50% blends of the thermoplastics PLA and polyvinylidene fluoride (PVDF) as well as samples with the PLA-based copolymers at the IRIS beamline of BESSY II.

Read nore on HZB website

Image: In nano-IR imaging, the layer structures of the pure PVDF/PLLA mixture (left) and with the SAD additive (right)  are clearly distinguishable. The light and dark colours correspond to the PLLA and PVDF phases, respectively. When SAD is added, the domain sizes of the two phases are reduced.

Credit: TU Eindhoven/HZB

Hydrogen: Breakthrough in alkaline membrane electrolysers

Hydrogen: Breakthrough in alkaline membrane electrolysers

A team from the Technical University of Berlin, HZB, IMTEK (University of Freiburg) and Siemens Energy has developed a highly efficient alkaline membrane electrolyser that approaches the performance of established PEM electrolysers. What makes this achievement remarkable is the use of inexpensive nickel compounds for the anode catalyst, replacing costly and rare iridium. At BESSY II, the team was able to elucidate the catalytic processes in detail using operando measurements, and a theory team (USA, Singapore) provided a consistent molecular description. In Freiburg, prototype cells were built using a new coating process and tested in operation. The results have been published in the prestigious journal Nature Catalysis.

Hydrogen will play a major role in the energy system of the future, as an energy storage medium, a fuel and valuable raw material for the chemical industry. Hydrogen can be produced by electrolysis of water in a virtually climate-neutral way, provided this is done with electricity from solar or wind power. Scale-up efforts for a green hydrogen economy are currently largely dominated by two systems: proton-conducting membrane electrolysis (PEM) and classic liquid alkaline electrolysis. AEM electrolysers combine the advantages of both systems and, for example, do not require rare precious metals such as iridium.

Alkaline Membrane (AEM) Electrolysers without Iridium

Now, research teams from TU Berlin and HZB, together with the Department of Microsystems Engineering (IMTEK) at the University of Freiburg and Siemens Energy, have presented the first AEM electrolyser that produces hydrogen almost as efficiently as a PEM electrolyser. Instead of iridium, they used nickel double hydroxide compounds with iron, cobalt or manganese and developed a process to coat them directly onto an alkaline ion exchange membrane.

Read more on HZB website

Image:The AEM water electrolyser cell works with a newly developed membrane electrode (MEA) that is directly coated with a nickel-based anode catalyst. Its molecular mode of action has been elucidated, and the AEM cell has proven to be almost as powerful as a conventional PEM cell with iridium catalyst.

Credit: Flo Force Fotografie, Hahn-Schickard & IMTEK Universität Freiburg

Alternating currents for alternative computing with magnets

Alternating currents for alternative computing with magnets

A new study conducted at the University of Vienna, the Max Planck Institute for Intelligent Systems in Stuttgart, and the Helmholtz Centers in Berlin and Dresden takes an important step in the challenge to miniaturize computing devices and to make them more energy-efficient. The work published in the renowned scientific journal Science Advances opens up new possibilities for creating reprogrammable magnonic circuits by exciting spin waves by alternating currents and redirecting these waves on demand. The experiments were carried out at the Maxymus beamline at BESSY II.

The central processing units (CPUs) that we use in our laptops, desktops or even phones are using billions of transistors, which are based on the complementary metal oxide semiconductor (CMOS) technology. With the increasing need to miniaturize these devices, several physical limitations are raising concerns for their sustainability. In addition, high power consumptions and energy losses, push scientists to search for alternative computing architectures.

One of the promising candidates are magnons, the quanta of spin waves. “Imagine a calm lake. If we let a stone fall into water, the resulting waves will propagate away from the point of generation. Now, we replace the lake with a magnetic material and the stone with an antenna. The propagating waves are called spin waves and can be used to transfer energy and information from one point to another with minimal losses,” says Sabri Koraltan from the University of Vienna, first author of the recent study published in the journal Science Advances. Once generated, the spin waves can be used for magnonic devices to perform classical and unconventional computing tasks. “To reduce the footprint of magnonic devices, we need to use spin waves with short wavelengths, which are difficult to generate using state-of-the-art nano antennas due to limited efficiency,” adds Sebastian Wintz from Helmholtz-Zentrum Berlin and the coordinator of the research project. Nano antennas can only be fabricated in clean rooms, highly specialized nanofabrication facilities, using advanced lithography techniques. 

Read more on HZB website

BESSY II: Heterostructures for Spintronics

BESSY II: Heterostructures for Spintronics

Spintronic devices work with spin textures caused by quantum-physical interactions. A Spanish-German collaboration has now studied graphene-cobalt-iridium heterostructures at BESSY II. The results show how two desired quantum-physical effects reinforce each other in these heterostructures. This could lead to new spintronic devices based on these materials.

Spintronics uses the spins of electrons to perform logic operations or store information. Ideally, spintronic devices could operate faster and more energy-efficiently than conventional semiconductor devices. However, it is still difficult to create and manipulate spin textures in materials.

Graphene for Spintronics

Graphene, a two-dimensional honeycomb structure build by carbon atoms, is considered an interesting candidate for spintronic applications. Graphene is typically deposited on a thin film of heavy metal. At the interface between graphene and heavy metal, a strong spin-orbit coupling develops, which gives rise to different quantum effects, including a spin-orbit splitting of energy levels (Rashba effect) and a canting in the alignment of spins (Dzyaloshinskii-Moriya interaction). Especially the spin canting effect is needed to stabilise vortex-like spin textures, known as skyrmions, which are particularly suitable for spintronics.

Plus Cobalt Monolayers

Now, however, a Spanish-German team has shown that these effects are significantly enhanced when a few monolayers of the ferromagnetic element cobalt are inserted between the graphene and the heavy metal (here: iridium). The samples were grown on insulating substrates which is a necessary prerequisite for the implementation of multifunctional spintronic devices exploiting these effects.

Read more on HZB website

Image: Symbolic illustration of a graphene layer on a microchip. In combination with a heavy-metal thin film and ferromagnetic monolayers, graphene could enable spintronic devices.

Credit: Dall-E/arö

Green hydrogen: MXenes shows talent as catalyst for oxygen evolution

Green hydrogen: MXenes shows talent as catalyst for oxygen evolution

The MXene class of materials has many talents. An international team led by HZB chemist Michelle Browne has now demonstrated that MXenes, properly functionalised, are excellent catalysts for the oxygen evolution reaction in electrolytic water splitting. They are more stable and efficient than the best metal oxide catalysts currently available. The team is now extensively characterising these MXene catalysts for water splitting at the Berlin X-ray source BESSY II and Soleil Synchrotron in France.

Green hydrogen is seen as one of the energy storage solutions of the future. The gas can be produced in a climate-neutral way using electricity from the sun or wind by electrolytic water splitting. While hydrogen molecules are produced at one electrode, oxygen molecules are formed at the other. This oxygen evolution reaction (OER) is one of the limiting factors in electrolysis. Special catalysts are needed to facilitate this reaction. Among the best candidates for OER catalysts are, for example, nickel oxides, which are inexpensive and widely available. However, they corrode quickly in the alkaline water of an electrolyser and their conductivity also leaves much to be desired. This is currently preventing the development of low-cost, high-performance electrolysers.

MXene as catalysts

A new class of materials could offer an alternative: MXenes, layered materials made of metals, such as titanium or vanadium, combined with carbon and/or nitrogen. These MXenes have a huge internal surface area that can be put to fantastic use, whether for storing charges or as catalysts.

An international team led by Dr Michelle Browne has now investigated the use of MXenes as catalysts for the oxygen evolution reaction. PhD student Bastian Schmiedecke chemically ‘functionalised’ the MXenes by docking copper and cobalt hydroxides onto their surfaces. In preliminary tests, the catalysts produced in this way proved to be significantly more efficient than the pure metal oxide compounds. What’s more, the catalysts showed no degradation and even improved efficiency in continuous operation.

Read more on HZB website

Image: The surface of a Vanadium carbide MXene has been examined by Scanning Electron Microscopy. The beautiful structures are built by cobalt copper hydroxide molecules.

Credit: B. Schmiedecke/HZB

Green hydrogen from direct seawater electrolysis

Green hydrogen from direct seawater electrolysis

At first glance, the plan sounds compelling: invent and develop future electrolysers capable of producing hydrogen directly from unpurified seawater. But a closer look reveals that such direct seawater electrolysers would require years of high-end research. And what is more: DSE electrolyzers are not even necessary – a simple desalination process is sufficient to prepare seawater for conventional electrolyzers. In a commentary in Joule, international experts compare the costs and benefits of the different approaches and come to a clear recommendation.

Fresh water is a limited resource; more than 96% of the world’s water is found in the oceans. If seawater could be fed directly into a future electrolyser to produce green hydrogen using renewable energy from the wind or sun, it sounds like a very good solution. Hundreds of millions of dollars in research fundingare spend for this idea and, in 2023 alone, there have been more than 500 publications (this number is growing exponentially) on direct seawater electrolysis.

No need for new development

However, a techno-economic analysis shows that this argument collapses as soon as the costs and benefits are analysed in more detail. “There is no convincing reason to develop DSE technology because there are already efficient solutions for using seawater to produce hydrogen,” says Dr Jan Niklas Hausmann, electrolysis researcher at HZB and lead author of the Joule commentary. International experts from various disciplines from renowned research institutions such as Yale University, universities in Canada, Germany and HZB contributed to the commentary.

Proven methods work

It is already possible to use seawater to produce hydrogen. Proven processes such as reverse osmosis can be used to purify seawater for “normal”, commercially available electrolysers. From a thermodynamic point of view, the purification of seawater needs only 0.03% of the energy required for its electrolysis. This is also reflected in the current cost: purifying seawater to produce one kilogram of hydrogen costs less than two cents. However, one kilogram of hydrogen costs 13.85 euros at German filling stations.

Read more on HZB website

All BESSY II instruments reconnected to the network

All BESSY II instruments reconnected to the network

Thirteen months ago, HZB fell victim to a criminal cyberattack that also took BESSY II light source and the instruments in the experimental hall out of operation. BESSY II was up and running again after just three weeks and the instruments were gradually put back into operation. Now HZB can report some good news: All experimental stations are again integrated into the new IT networks and can record data.

In a task force led by Andreas Jankowiak and Jens Viefhaus, a team led by Ruslan Ovsyannikov succeeded in implementing a new IT infrastructure and a resilient network architecture. This project is now to be firmly established and perpetuated at HZB. The aim is to achieve the full functionality of the BESSY-II user service, to establish new possibilities for remote experiments and better data management.

Read more on HZB website

Image: HZB

Credit: D. Laubner

A new way to control the magnetic properties of rare earth elements

A new way to control the magnetic properties of rare earth elements

The special properties of rare earth magnetic materials are due to the electrons in the 4f shell. Until now, the magnetic properties of 4f electrons were considered almost impossible to control. Now, a team from HZB, Freie Universität Berlin and other institutions has shown for the first time that laser pulses can influence 4f electrons- and thus change their magnetic properties. The discovery, which was made through experiments at EuXFEL and FLASH, opens up a new way to data storage with rare earth elements.

The strongest magnets we know of are based on rare earths. Their 4f electrons are responsible for their magnetic properties: they generate a large magnetic moment that is maintained even when their chemical environment changes. This means that rare earths can be used in very different compounds and alloys without changing their special magnetic properties. Until now, it was assumed that the magnetic properties of 4f electrons could not be changed even if the material was excited with a laser pulse. But indeed, this is possible, as a team from HZB, Freie Universität Berlin, DESY, the European X-ray laser XFEL and other institutions has now shown: The spatial arrangement of the 4f electrons can be briefly switched by laser excitation. This also changes their magnetism. This effect opens up new possibilities for the fast and energy-efficient control of magnetic rare-earth materials. The work has now been published in the journal Science Advances.

Read more on HZB website

Image: The image shows the terbium orbitals between which the excitation takes placeand a schematic sketch of the excitation process. 

Credit: HZB

BESSY II shows how solid-state batteries degrade

BESSY II shows how solid-state batteries degrade

Solid-state batteries have several advantages: they can store more energy and are safer than batteries with liquid electrolytes. However, they do not last as long and their capacity decreases with each charge cycle. But it doesn’t have to stay that way: Researchers are already on the trail of the causes. In the journal ACS Energy Letters, a team from HZB and Justus-Liebig-Universität, Giessen, presents a new method for precisely monitoring electrochemical reactions during the operation of a solid-state battery using photoelectron spectroscopy at BESSY II. The results help to improve battery materials and design.

Solid-state batteries use a solid ion conductor between the battery electrodes instead of a liquid electrolyte, which allows lithium to be transported during charging and discharging. This has advantages including increased safety during operation and generally higher capacity.  However, the lifetime of solid-state batteries is still very limited. This is because decomposition products and interphases form at the interfaces between the electrolyte and the electrode, which hinders the transport of the lithium ions and leads to consumption of active lithium so that the capacity of the batteries decreases with each charge cycle.

What happens during operation?

Now a team led by HZB researchers Dr. Elmar Kataev and Prof. Marcus Bär has developed a new approach to analyse the electrochemical reactions at the interface between solid electrolyte and electrode with high temporal resolution. Kataev explains the research question: “Under what conditions and at what voltage do such reactions occur, and how does the chemical composition of these intermediate phases evolve during cell operation?”

Best candidate LiPSCl examined

For the study, they analysed samples of the solid electrolyte Li6PS5Cl, a material that is considered the best candidate for solid-state batteries as it possesses high ionic conductivity. They worked closely with the team of battery expert Professor Jürgen Janek from the Justus Liebig University Giessen (JLU Giessen). An extremely thin layer of nickel (30 atomic layers or 6 nanometres) served as the working electrode. A film of lithium was pressed onto the other side of the Li6PS5Cl pellet to act as a counter electrode.

Read more on HZB website

Image: SEM images of LPSCl pellets before (left) and after (right) the operando HAXPES experiment

From waste to value: The right electrolytes can enhance glycerol oxidation

From waste to value: The right electrolytes can enhance glycerol oxidation

When biomass is converted into biodiesel, huge amounts of glycerol are produced as a by-product. So far, however, this by-product has been little utilised, even though it could be processed into more valuable chemicals through oxidation in photoelectrochemical reactors. The reason for this: low efficiency and selectivity. A team led by Dr Marco Favaro from the Institute for Solar Fuels at HZB has now investigated the influence of electrolytes on the efficiency of the glycerol oxidation reaction. The results can help to develop more efficient and environmentally friendly production processes.

In 2023, around 16 billion litres of biodiesel and HVO diesel were produced in the European Union*, based on maize, rapeseed, or partially on waste materials from agricultural production. A by-product of biodiesel production is glycerol, which can be used as a building block for the production of valuable chemicals such as dihydroxyacetone, formic acid, glyceraldehyde and glycolaldehyde via a glycerol oxidation reaction (GOR). Glycerol can be oxidised electrochemically in (photo)electrochemical (PEC) reactors, which are currently being developed in particular for the production of green hydrogen. However, this path in PEC-plants is still hardly exploited at present, even though it could significantly increase the economic efficiency of the PEC Power-to-X process, since the oxidation of glycerol requires a much lesser energy input than hydrogen production through water splitting, but at the same time produces more valuable chemicals.

Many studies have already investigated the role of photocatalysts in PEC electrolyzers, while the role of the electrolyte had not yet been systematically analysed. A team led by Dr Marco Favaro at the Institute for Solar Fuels has now unveiled the influence of electrolyte composition on the efficiency and stability of the glycerol oxidation.

Read more on HZB website

Image: The glycerol’s hydroxyl groups are attracted to the Bi3+ ions on the surface of the BiVO4 photoanode. The electrolyte plays a decisive role in mediating these interactions.

Credit: HZB

Small powerhouses for very special light

Small powerhouses for very special light

An international team presents the functional principle of a new source of synchrotron radiation in Nature Communications Physics. Steady-state microbunching (SSMB) allows to build efficient and powerful radiation sources for coherent UV radiation in the future. This is very attractive for applications in basic research as well in the semiconductor industry.

When ultrafast electrons are deflected, they emit light – synchrotron radiation. This is used in so called storage rings in which magnets force the particles onto a closed path. This light is longitudinally incoherent and consists of a broad spectrum of wavelengths. Its high brilliance makes it an excellent tool for materials research. Monochromators can be used to pick out individual wavelengths from the spectrum, but this reduces the radiant power by many orders of magnitude to values of a few watts only.

Size matters

But what if a storage ring were instead to deliver monochromatic, coherent light with outputs of several kilowatts, analogous to a high-power laser? Physicist Alexander Chao and his doctoral student Daniel Ratner found an answer to this challenge in 2010: if the electron bunches orbiting in a storage ring become shorter than the wavelength of the light they emit, the emitted radiation becomes coherent and therefore millions of times more powerful.

Read more on HZB website

Image: Jörg Feikes and PhD student Arnold Kruschinski in the control room of BESSY II and the MLS.

Credit: Ina Helms / HZB

MXenes for energy storage: Chemical imaging more than just surface deep

MXenes for energy storage: Chemical imaging more than just surface deep

A new method in spectromicroscopy significantly improves the study of chemical reactions at the nanoscale, both on surfaces and inside layered materials. Scanning X-ray microscopy (SXM) at MAXYMUS beamline of BESSY II enables the investigation of chemical species adsorbed on the top layer (surface) or intercalated within the MXene electrode (bulk) with high chemical sensitivity. The method was developed by a HZB team led by Dr. Tristan Petit. The scientists demonstrated among others first SXM on MXene flakes, a material used as electrode in lithium-ion batteries.

Since their discovery in 2011, MXenes have gathered significant scientific interest due to their versatile tunable properties and diverse applications, from energy storage to electromagnetic shielding. Researchers have been working to decipher the complex chemistry of MXenes at the nanoscale.

The team of Dr. Tristan Petit now made a significant progress in MXene characterization, as described in their recent publication. They utilized SXM to investigate the chemical bonding of Ti3C2Tx MXenes, with Tx denoting the terminations (Tx=O, OH, F, Cl), with high spatial and spectral resolution. The novelty in this work is to combine simultaneously two detection modes, transmission and electron yield, enabling different probing depths.

SXM provided detailed insights into the chemical composition and structure of MXenes. According to Faidra Amargianou, first author of the study: “Our findings shed light on the chemical bonding within MXene structure, and with surrounding species, offering new perspective for their utilization across various applications, especially in electrochemical energy storage.”

Read more on HZB website

Image: Scanning X-ray images of a dismounted Li-ion battery with cycled MXene electrode (green), electrolyte/ carbonate species (red) and separator (yellow). The Transmission (bulk-sensitive) image is on the left, the electron yield (surface-sensitive) image on the right.

Credit: HZB